This invention relates to an indicator arrangement for a marine propulsion engine and more particular to an improved oil pressure warning indicator for a marine propulsion system.
In many forms of marine propulsion systems, there are provided certain warnings, indicators or warning devices positioned in proximity to the operator's area that provide an indication to the operator that there is a malfunction in the engine propulsion system. For example, in watercraft powered by outboard motors having four cycle engines, there may be provided an oil pressure warning light or other type of warning device that gives a signal to the operator when the engine oil pressure falls below a predetermined value. The types of devices provided for this purpose heretofore, however, have had a problem in that the sensitivity of the oil pressure switch is such that improper signals may be given and/or it may be necessary to replace the switch more frequently than is desired.
The problem dependent with this prior art type of construction can be understood by reference primarily to FIGS. 1 and 2 which show, respectively, the type of circuitry employed for this purpose in the prior art and the type of oil pressure switch utilized, which is shown partially and in cross-section.
Referring specifically to FIG. 1, the reference numeral 11 indicates schematically the outboard motor and specific components of it are shown in electrical diagram form. The outboard motor 11 is connected to the hull of an associated watercraft which is indicated at 12 for propelling it in a manner known in the art.
Associated with the outboard motor 11 is a magneto generator or alternator, indicated generally by the reference numeral 13, which includes a charging coil 14 in which an electrical current is induced. This current is transferred through a rectifier diode bridge 15 and a quick disconnect electrical coupling 16 to the watercraft hull 12 for charging a battery, indicated at 17, through a hull side electrical circuit, indicated at 18. This electrical circuit 18 also provides power to other hull side devices.
The electrical circuit includes a main switch 19 by which electrical power is transmitted to an ignition control circuit 21 of the outboard motor through a further quick disconnect electrical connector 22. The ignition control circuit 21 includes an arrangement which fires a group of spark plugs 23 by energizing the primary windings of spark coils 24 in a manner that is well known in this art. Pulser coils 25 of the magneto generator provide timing signals by which the ECU 21 controls the timing of firing of the spark plugs 23 in any conventionable manner.
A kill switch 26 is also mounted within the watercraft hull 12 for discontinuing the operation of the engine, for example, by grounding out the ignition circuit of the ECU 21 in a manner also known in this art.
The electrical power supplied by the rectifier circuit 13 to the watercraft hull 12 is utilized to power various loads indicated schematically at 27 and other devices as indicated also in this figure. Among these loads is an oil pressure warning light 28 or other type of warning device that provides an indication to the watercraft operator when the oil pressure of the engine or some other condition is not within a predetermined value. Specifically with a low oil pressure warning, this oil pressure signal is sent by a switch, indicated at 29, and which is shown in cross-section in FIG. 2.
As may be seen, the switch 29 is comprised of a housing having a base piece 31 and a main housing piece 32, which pieces define a pressure chamber 33. The base piece 31 is tapped into the engine body and has a pressure sensing port 34 to which oil circulated by the engine lubricating systems is delivered through a suitable conduit.
A switch comprised of a fixed terminal 35 and a movable terminal 36 are provided in the cavity 33 and sense the oil pressure from the line 34. A coil compression spring 37 urges the movable terminal 36 into contact with the fixed terminal 35. This spring 37 also provides an electrical connection to a conductor 38 which is connected to the ground as shown schematically in FIG. 1.
When the oil pressure is above a predetermined level, the movable switch element 36 will be biased away from the fixed contact 35 and the electrical circuit which passes through the indicator light 28 will be open. However, if the oil pressure falls below this predetermined value, the spring 37 will urge the movable contact 36 into contact with the fixed terminal 35 to ground this circuit so that the light 28 will be illuminated.
There are two rather distinct problems with this type of prior art construction. The first is that the electrical current that is applied to the terminals 35 and 36 is basically the same as the amount of electrical current that can pass through the warning light 28 to maintain it in its illuminated condition. Thus, the characteristics and limitations of the lamp 28 determines the maximum current flow that can pass through the switch 29.
This is disadvantageous because of the fact that the terminals will deteriorate with time and, accordingly, the switch may become inoperable. Because the terminal contacts 35 and 36 are continuously immersed in oil, the surfaces can become oxidized over time or fatigue of the spring may weaken it to cause the conductivity between the terminals to become deteriorated. Although this problem can be solved by increasing the current flow, as noted, this is limited by the lamp 28 and thus is not a feasible alternative.
Of course, higher quality or non-corrosion resisting terminals, such as gold-plated or gold terminals can be employed, but this makes the cost of the sensor 29 too high.
It is, therefore, a principle of object of this invention to provide an improved indicator arrangement for a marine propulsion unit wherein the sensing switch can be supplied with a higher current flow than that which actually actuates the warning device.
It is a further of object of this invention to provide an improved indicator arrangement for a marine propulsion unit wherein the sensing switch is supplied with a source of electrical current that can be different than that which actually actuates the warning device.